Method of Controlling a Rotatable-Drum Laundry Dryer and a Rotatable-Drum Laundry Dryer Implementing the Method

ABSTRACT

A method is provided for controlling a drying operation of a rotatable-drum laundry dryer ( 1 ) having a rotatable drum ( 3 ) for loading laundry ( 5 ) and at least an electrode sensor ( 22 ) for sensing dryness of the laundry ( 5 ). The method includes the step of detecting the presence/absence of moist laundry ( 5 ) inside the rotatable drum ( 3 ) by the electrode sensor ( 22 ). If a presence of moist laundry inside the rotatable drum ( 3 ) is detected, a drying cycle is started. The dryness of the laundry ( 5 ) is sensed during the drying cycle and a cycle time (TD) at which the sensed dryness reaches a preset dryness threshold is measured. If the cycle time (TD) is lower than a preset dryness threshold time (Sm), the drying cycle is continued for a first additional time (D1), and the drying cycle is stopped at the end of the first additional time (D1).

The present invention relates to a method of controlling arotatable-drum laundry dryer and a rotatable-drum laundry dryerimplementing the method.

Methods of controlling rotatable-drum laundry dryers are known, inwhich: hot air is fed into the rotatable drum so as to flow over thelaundry inside the drum; an electric parameter associated with thelaundry moisture is measured by means of an electrode sensor arranged inorder to contact with the laundry when drum rotates; the dryness of thelaundry is determined according to the measured electric parameter; andthe drying cycle is stopped when the measured electric parameter reachesa preset value associated with a prefixed final dryness.

More specifically, laundry dryers are known comprising an electroniccontrol unit which receives a plurality of voltage signals having anamplitude and/or a frequency associated with the electric parameter ofthe laundry, i.e. impedance or resistance, or conductance, and measureda prefixed number of times; the electronic control unit determines thedryness of the laundry according to the measured voltage signals, andcontrols the drying cycle according to determined laundry dryness. Forexample the electrode sensor may be configured to output a voltagesignal which is proportional to the dryness of the laundry. Thus, moredried is the laundry, higher is its electric parameter and consequentlybigger is the voltage signal outputted from the electrode sensor.

The technical problem of the above-described prior-art laundry dryer isthat when contacts between laundry and electrode sensor, during thedrying cycle, are very few, an incomplete dryness condition of thelaundry may be performed, since the electronic control unit mayerroneously conclude (or determine, resolve) that the few number ofcontacts between the laundry and the electrode corresponds to a drycondition of the laundry.

As a matter of the fact, research by the Applicant shows that when theabove control method is performed in a rotary-drum home laundry dryer inwhich the electrode sensor is arranged outside the drum, i.e. in aposition facing the opening in the drum, the frequency with which thelaundry contacts the electrode sensor is reduced, or tends towards zero,when, for example, the laundry corresponds to a small load quantity,i.e. a single T-shirt, or when, for example, a “special” kind of laundry(e.g. a pillow), is loaded in the laundry dryer in such a way that itgets stuck inside the drum in such a position that it doesn't contact oronly rarely contacts the electrode sensor.

In such cases, because the number of contacts laundry-electrode is veryfew and/or the electric signals outputted from electrode sensor areaffected by high electric noise, the electronic control unit determinesa high average value and, as a consequence, calculates a high electricparameter (impedance or resistance or conductance), and erroneouslyassociate the latter with a dryness condition. Thus, electronic controlunit may incorrectly conclude (or determine, resolve) that an expecteddrying condition of the laundry has been reached, and it may and stopthe drying cycle too early, even if the laundry is still wet.

JP2000229200 discloses a clothes drying machine in which dryingoperation are controlled in the case of a small amount of laundry intothe rotating drum. In particular, the drying machine is configured tostart a drying course by measuring the number of contacts betweenelectrode and laundry; to determine whether the laundry is a high loador small load based on the measured number of contacts; and if thedetermined laundry is a small load, to set the drying cycle period fortwenty-five minutes, independently of the moisture of the laundry.

JP6312095 discloses a clothes drying machine which dries laundryindependently of the its quantity, by executing the drying operation bya drying time setting timer when a small quantity signal is outputtedfrom a clothes quantity judging device, while executing the dryingoperation, monitoring the dried state if the small quantity signal isnot outputted. In detail, the clothes are agitated, and each time whenthe clothes come to an electrode which operates as clothes detector, isdetected repeatedly. When the clothes detection signal which is detectedup to the time-up of a clothes quantity judging timer is less than astandard value, a microcomputer incorporated in a control circuitoutputs a small quantity signal from a clothes quantity judging deviceand forcibly executes the drying operation without monitoring the driedstate of the clothes up to the time-up of a drying time setting timer.Under the condition that it is considered that the contact frequency ofthe clothes with the electrode is high and the reliability of the signalof the electrode is high, the drying operation is executed, judging thedegree of dryness by the electrode.

Clothes drying machines disclosed in JP2000229200 and in JP6312095 havethe problem that systems starts the drying cycle selected by the userand maintains operating the same in any case for a preset time, even ifthe drum is empty or the laundry is already dry, causing a uselesswastage of electric energy.

It is therefore an object of the present invention to provide a solutiondesigned to obviate one or more problems due to limitations anddisadvantages of the related art, and in particular a solution whichguarantees the user to control the rotatable-drum laundry dryer in orderto assure a uniform laundry dryness, even if the laundry inside of thedrum is few and/or is arranged inside the rotatable-drum so that numberof contacts with the electrode sensor is very low, and at the same timestrongly reducing the wastage of electric energy, in particular in caseno laundry or already dry laundry is loaded in the rotatable drum.

According to the present invention, there is provided a method ofcontrolling a drying operation of a rotatable-drum laundry dryercomprising a rotatable drum for loading laundry and at least anelectrode sensor for sensing dryness of the laundry. The methodcomprises: detecting the presence/absence of moist laundry inside therotatable drum by the electrode sensor; if presence of moist laundryinside the rotatable drum is detected, starting a drying cycle; sensingdryness of the laundry during the drying cycle; measuring a cycle timeat which the sensed dryness reaches a preset dryness threshold; if thecycle time is lower than a preset dryness threshold time, continuing thedrying cycle for a first additional time, and stopping the drying cycleat the end of the first additional time.

Preferably the first additional time is such that the time elapsed fromthe beginning of the drying cycle and the stopping of the drying cycleis a preset minimum dryness time.

More preferably the first additional time is set as the difference fromthe preset minimum dryness time and the cycle time.

Advantageously the method comprises: if the cycle time is not lower thanthe preset dryness threshold time, continuing the drying cycle for apreset second additional time; and stopping the drying cycle at the endof the second additional time.

Preferably the second additional time is between zero and ten seconds.

Preferably determining the presence/absence of moist laundry inside therotatable-drum comprises: performing a starting detection phase for astarting detection time; if no moist laundry has been detected duringthe starting detection time, performing one or more additional detectionphases, each of which lasts an additional detection time; if no moistlaundry has been detected during the additional detection phase/s,ending operation of rotatable-drum laundry dryer.

Advantageously the additional detection time is lower than the startingdetection time.

The invention regards also a rotatable-drum laundry drier comprising: arotatable drum for loading laundry, a least an electrode sensor forsensing dryness of the laundry; feeding drying air means for feedingdrying air into the drum, and rotating means for rotating the drum aboutan axis of rotation. The rotatable-drum dryer comprises electroniccontrol means configured to: detect presence/absence of moist laundryinside the rotatable drum by the electrode sensor; if presence of moistlaundry inside rotatable drum is detected, start a drying cycle; sensedryness of the laundry during the drying cycle; measure a cycle time atwhich the sensed dryness reaches a preset dryness threshold; if thecycle time is lower than a preset dryness threshold time, continue toperform the drying cycle for a first additional time, and stop thedrying cycle at the end of the first additional time.

Advantageously the first additional time is such that the time elapsedfrom the beginning of the drying cycle and the stopping of the dryingcycle is a preset minimum dryness time.

Preferably the first additional time is set as the difference from thepreset minimum dryness time and the cycle time.

Opportunely the electronic control means are further configured to:continue to perform the drying cycle for a preset second additionaldryness time if the cycle time is not lower than the preset drynessthreshold time; and stop the drying cycle at the end of the presetsecond increased cycle time.

Advantageously the second additional time is between zero and tenseconds.

Preferably the electronic control means are further configured to:perform a starting detection phase for a starting detection time; if nomoist laundry has been detected during the starting detection time,perform one or more additional detection phases; and if moist laundryhave been detected during the additional detection phase/s, endoperation of rotatable-drum laundry drier.

Advantageously each of the one or more additional detection phases lastsan additional detection time lower than the starting detection time.

A non-limiting embodiment of the present invention will be described byway of example with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic lateral cross section of a rotatable-drumlaundry drier implementing the laundry drying control method accordingto the present invention;

FIG. 2 shows an inner lateral wall of the FIG. 1 rotatable-drum laundrydrier; while

FIG. 3 shows an operation flow chart of the control method implementedaccording to the present invention.

Number 1 in FIG. 1 indicates as a whole a rotatable-drum laundry dryercomprising an outer casing 2, which preferably rests on the floor on anumber of feet.

Casing 2 supports a rotatable laundry drum 3, which defines a dryingchamber 4 for laundry 5 and rotates about a preferably, though notnecessarily, horizontal axis of rotation 6. In an alternative embodimentnot shown, axis of rotation 6 may be vertical or inclined.

Drying chamber 4 has a preferably frontal access opening 7 closable by adoor 8 preferably hinged to casing 2.

Drum 3 may be rotated about axis of rotation 6 by an electric motor,schematically represented in FIG. 1 and indicated with reference number9, is fed with hot air heated by a heating device, schematicallyrepresented in FIG. 1 and indicated with reference number 10, and is fedinto drum 3 preferably by a fan schematically represented in FIG. 1 andindicated with reference number 11. Fan 11 may preferably, though notnecessarily, be driven by electric motor 9 or, in an alternativeembodiment (not shown), by an auxiliary electric motor (not shown)independent of electric motor 9.

In the FIG. 1 example, one opened side of the drum 3 of the laundrydrier 1 is advantageously associated, in a rotatable and substantiallyair-tight way, to a perforated inner wall 12 fixed to a lateral wall ofcasing 2 and through which hot air flows into drum 3; the other openedside of the drum 3 is advantageously associated, in a rotatable andsubstantially air-tight way, to a flange 13 associated to casing 2 andinterposed between door 8 and front access opening 7 of drum 3.

In the FIGS. 1 and 2 example, flange 13 is fixed firmly to casing 2, andis positioned at front access opening 7 so as to project at least partlyinside drum 3, so that its inner surface faces the laundry 5 when thelatter is loaded into the drum 3.

Heating device 10 may advantageously comprise one or more electricheating components, such as electric resistors (not shown) or, in analternative embodiment, a heat pump.

In actual use, fan 11 blows a stream of drying air (represented by thewhite arrows in FIG. 1), produced by heating device 10, preferablythrough perforated inner wall 12 into drum 3. After contacting laundry 5inside drum 3, the moisture-laden drying air flows out of drum 3 and itis preferably directed to a condensing device 15, which cools the dryingair to condense the moisture inside it. For this purpose, condensingdevice 15 may be supplied with cold air from outside the drier, andfeeds the moisture-free air to fan 11. It should be pointed out thatcondensing device 15 as described above applies, purely by way ofexample, to one possible embodiment of the present invention, and may beomitted in the case of an exhaust-type rotatable-drum laundry drier 1(i.e. in which the hot and moisture-laden drying air from the rotatablelaundry drum 3 is expelled directly out of rotatable-drum laundry drier1).

The rotatable-drum laundry drier 1 also comprises an electronic controlsystem 16, which is configured to control the rotatable-drum laundrydrier 1, advantageously on the basis of a drying cycle selected by auser via a user control interface 18.

The electronic control system 16 advantageously comprises an electrodesensor 22 for detecting dryness of the laundry.

According to a preferred embodiment, the electrode sensor 22 is acontact electrode sensor type and comprises two metal plates 23 arrangedon the flange 13 in a position facing the inside of the drum 3, forsensing the dryness of laundry by using impedances generated at oppositeends of the metal plates 23 according to moisture content of the laundry5 when the later is brought into contact with the opposite metal plates23, and forwards the dryness as a electrical signal, i.e. a voltagesignal. Nevertheless, it is obvious that electrical signal outputted bythe electrode sensor 22 could be associated, for example, with theresistance and/or conductance of the laundry 5 sensed between the metalplates 23.

Preferably the electrode sensor is configured to generate an oscillatingelectrical signal and vary the frequency of oscillation of theelectrical signal according to the laundry moisture/dryness.

The electronic control system 16 further comprises an electronic controlunit 14, which is configured to control the electric motor 9, heatingdevice 10 and/or fan 11 in order to regulate the rotation speed of thedrum 3, the temperature and/or the flow rate of hot air entering thedrum 3 according to preset temperatures and flow rates specified for thelaundry drying cycle selected by the user.

Preferably, selectable laundry cycles may comprise for example, a“cotton laundry drying cycle”, a “synthetic fabric laundry dryingcycle”, a “wool laundry drying cycle”, and a “delicate laundry dryingcycle”.

The electronic control unit 14 is further configured to:

-   -   detect the presence/absence of moist laundry 5 inside the        rotatable drum 3 by the electrode sensor 22;    -   if presence of moist laundry 5 inside the rotatable drum 3 is        detected, start a drying cycle that user selected.

Advantageously, if presence of moist laundry 5 inside the rotatable drum3 is not detected, the electronic control unit 14 stops operation of therotatable-drum laundry dryer 1.

It should be pointed out that “detecting the presence/absence of moistlaundry 5 inside the rotatable drum 3” comprises both simply detectingthe presence/absence of laundry inside the drum 3 (i.e. independently onthe moisture of the laundry), and detecting the presence/absence oflaundry having a prefixed degree of moisture (or in other words having aprefixed degree of dryness).

In other words the electronic control unit 14 is configured to sense (byusing the electric signals coming from the electrode sensor 22) both ifthere is laundry or not inside the drum, and if the laundry is moist ornot, i.e. if the dryness of the laundry sensed by the electrode sensor22 is below or above a threshold value (DRL) which may preferably dependon the drying cycle selected by the user.

If laundry is not sensed at all, or if laundry is sensed, but itsdryness is above a prefixed threshold (DRL), i.e. if moist laundry hasnot been detected inside the drum 3, the drying cycle is not started,while if laundry is sensed, and its dryness is below a prefixedthreshold (DRL), i.e. if moist laundry has been detected inside the drum3, electronic control unit 14 starts the drying cycle that userselected.

The electronic control unit 14 is further configured to:

-   -   sense dryness of the laundry 5 during the drying cycle;    -   measure (or calculate, determine, estimate, detect) the cycle        time TD at which the sensed dryness reaches a preset dryness        threshold (which preferably depends on the specific laundry        cycle selected by the user);    -   if the cycle time TD is lower than a preset dryness threshold        time (Sm), continue the drying cycle for a first additional time        D1,    -   stop the drying cycle at the end of this first additional time        D1.

Preferably the first additional time D1 is such that the time elapsedfrom the beginning of the drying cycle and the stopping of the dryingcycle is a preset minimum dryness time Tmin (e.g. 30 minutes).

More preferably the first additional time D1 is set as the differencefrom the preset minimum dryness time Tmin and the cycle time TD at whichthe sensed dryness reaches a preset dryness threshold (e.g. if TD is 10minutes, and Tmin is 30 minutes, then D1 is 20 minutes).

It should be pointed out that in the present application “drying cycle”indicates the part of the cycle starting when the heating device 10,i.e. electric resistor or heat pump, is switched-on for the first time,and ending when the heating device 10 is permanently switched-off.

During the “drying cycle” the heating device 10 may be continuouslyswitched on, or it may be repeatedly switched on and off according to atime pattern depending on the laundry cycle selected by the user.

Advantageously the above mentioned preset dryness threshold depends onthe laundry cycle selected by the user.

In other words, the electronic control unit 14 is configured to:

-   -   determine the presence/absence of moist laundry 5 inside the        rotatable drum 3 by using electric signal coming from electrode        sensor 22;    -   start a selected drying cycle if the rotatable drum 3 is not        empty and if the dryness of the loaded laundry is below a        certain prefixed threshold value (DRL) (or in other words if the        laundry moisture is above a certain prefixed threshold);    -   sense, preferably continuously, the dryness of the laundry, i.e.        based on the frequency of the electric signal outputted from the        electrode sensor 22;    -   compare sensed dryness with a preset dryness threshold, and        measure (or calculate, estimate, detect, determine) the cycle        time TD when sensed dryness reaches the preset dryness        threshold.

The electronic control unit 14 compares the cycle time TD when senseddryness reaches the preset dryness threshold with a preset drynessthreshold time Sm, and if the measured cycle time TD is lower than a thedryness threshold time Sm, electronic control unit 14 continues toperform the drying cycle for a certain time (first additional time D1),preferably for a period of time such that the time elapsed (e.g.measured) from the beginning of the drying cycle, reaches a presetminimum dryness time Tmin.

It is underlined that the phase of “detecting the presence/absence ofmoist laundry 5 inside the rotatable drum 3 and starting a drying cycleif presence of moist laundry 5 inside the rotatable drum 3 is detected”(while don't starting the drying cycle if presence of moist laundry 5inside the rotatable drum 3 is not detected) has a sort of synergiceffect with the phases of “measuring (or calculating, determining,estimating, detecting) the cycle time TD at which the sensed drynessreaches a preset dryness threshold and, if the cycle time TD is lowerthan a preset dryness threshold time (Sm), continuing the drying cyclefor a first additional time D1”; in fact if the phase of “detecting thepresence/absence of moist laundry 5 inside the rotatable drum 3 andstarting a drying cycle only if presence of moist laundry 5 inside therotatable drum 3 is detected” weren't comprised in the method, and ifthe user erroneously started a drying cycle without loading any piece oflaundry in the drum or loading already dry laundry, the drying cyclewould start and (for the reasons explained above with reference to theproblems of the prior art solutions) the sensed dryness would reach apreset dryness threshold very quickly, and therefore the drying cyclewould continue for a first additional time D1, with a further uselessenergy consumption.

Therefore the combination of the phases of “detecting thepresence/absence of moist laundry 5 inside the rotatable drum 3 andstarting a drying cycle only if presence of moist laundry 5 inside therotatable drum 3” and of “measuring (or calculating, determining,estimating, detecting) the cycle time TD at which the sensed drynessreaches a preset dryness threshold and, if the cycle time TD is lowerthan a preset dryness threshold time (Sm), continuing the drying cyclefor a first additional time D1” is very effective in solving the abovementioned problems of the prior art (i.e. obtaining a uniform laundrydryness even if the laundry inside of the drum is few and/or is arrangedinside the rotatable-drum so that number of contacts with the electrodesensor is very low, and at the same time strongly reducing the wastageof electric energy).

With reference to FIG. 3, an example of the operations implemented bythe control method performed by the electronic control system 16 madeaccording to the principles of the present invention shall now bedescribed.

In the initial phase (block 100), heating device 10 is turned-off, theelectronic control unit 14 recognises the selected drying cycle/programand preferably performs a detach phase, wherein it turns-on and controlsthe electric motor 9 to rotate the rotatable laundry drum 3 for a presetdetaching time so as to detach the laundry 5 from the inner surface ofthe rotatable laundry drum 3 for increasing the probability that laundry5 is brought into contact with the electrode sensor 22. According to thepreferred embodiment, the preset detaching time could be set between tenand twenty seconds, preferably about fifteen seconds.

The electronic control unit 14 performs a starting detection phase(block 110) for a starting detection time, during which it controls theelectric motor 9 to rotate the rotatable laundry drum 3 with presetrotation speed/s, and determines the presence/absence of the moistlaundry 5 inside the drum 3 based on the electric signal outputted fromthe electric sensor 22.

Preferably, electronic control unit 14 determinates (i.e. concludes orresolves) presence of moist laundry based on the impedance of thelaundry 5 sensed between the metal plates 23 and/or according to thefrequency of the electric signal outputted from the electrode sensor 22.

The electronic control unit 14 advantageously checks whether moistlaundry is present or absent inside of the drum 3 (block 120) based onpresence or absence condition is detected and in positive case (YESoutput from block 120) controls the rotatable-drum laundry dryer 1 inorder to perform the user selected drying cycle (block 130). In thatcase, electronic control unit 14 controls the electric motor 9, theheating device 10 and the fan 11 according to presetcontrol-parameters/control program associated with the drying cycle thatuser selected.

In negative case (NO output from block 120), the electronic control unit14 preferably sets a counter N=1 (block 140), performs an additionaldetection phase for an additional detection time ADT, e.g. thirtyseconds, during which it determinates, preferably by impedance sensed bythe electrode sensor 22 and/or according to the frequency of theelectric signal outputted from the electrode sensor 22 (block 150) ifmoist laundry is present or absent inside of the drum 3 (block 160).

Advantageously the additional detection time (ADT) is lower than thestarting detection time of the starting detection phase (block 110).

In negative case (NO output from block 160), the electronic control unit14 advantageously increases the counter N=N+1 (block 170), and checks ifincreased counter N=N+1 is equal or greater than a preset maximumthreshold N_(MAX), i.e. N>N_(MAX) (block 180).

In negative case (NO output from block 180), the electronic control unit14 performs again the additional detection phase for the additionaldetection time ADT (block 150), whereas in positive case (YES outputfrom block 180), the electronic control unit 14 confirms absence ofmoist laundry inside of the rotatable laundry drum 3 (i.e. according tothe electronic control unit 14 there is no moist laundry in the drum)and advantageously stops operation of the rotatable-drum laundry dryer1.

If the electronic control unit 14 detects a moist laundry presencecondition during the starting detection phase (YES output from block120) or one of the additional detection phases (YES output from block160), it controls the rotatable-drum laundry dryer 1 to perform theselected drying cycle (block 130).

In that case, electronic control unit 14 starts drying cycle byswitching-on/controlling the electric motor 9, the heating device 10 andthe fan 11.

During the drying cycle, the electrode sensor 22 provides voltagesignals associated with the moisture contents of the laundry 5 so as tosense the dryness of the laundry 5, the electronic control unit 14receives the electric signals from the electrode sensor 22 and measuresthe cycle time TD at which the sensed dryness reaches a preset drynessthreshold (block 190).

Advantageously, after starting the drying cycle, electronic control unit14 repeatedly senses the dryness of the laundry and compares, preferablycontinuously, sensed laundry dryness with the preset dryness threshold;the electronic control unit 14 measures (calculates, detects, obtains)the cycle time TD corresponding to the time at which sensed drynessreaches the preset dryness threshold.

The electronic control unit 14 checks if the cycle time TD is lower thana preset minimum dryness threshold time Sm (i.e. if TD<Sm) (block 200).

In positive case (YES output from block 200), i.e. the cycle time TD islower than the preset minimum dryness threshold time Sm, the electroniccontrol unit 14 concludes (or determines, resolves) an insufficientdryness condition, and continues to perform the drying cycle for a firstadditional time D1 (block 210), after which the drying cycle is stopped(block 220).

Preferably electronic control unit 14 sets the first additional time D1in such a way that the drying cycle ends when the time elapsed from thebeginning of the drying cycle reaches a preset minimum dryness timeTmin.

Advantageously the electronic control unit 14 sets the first additionaltime D1 as the difference between the preset minimum dryness time Tminand the cycle time TD at which sensed dryness reaches the preset drynessthreshold.

Regarding what has been described above, it should be pointed out thatduring the first additional time D1, the electronic control unit 14continues to keep switched on the electric motor 9, the fan 11 and theheating device 10 according to the selected drying cycle.

According to a preferred embodiment, the preset minimum dryness timeTmin may vary according to the selected drying cycle or may be a presetvalue, preferably comprised between twenty and thirty-five minutes,preferably about thirty minutes.

In negative case (No output from block 200), i.e. whether cycle time TDat which sensed dryness reaches the preset dryness threshold is equal orgreater than preset minimum dryness threshold time Sm, the electroniccontrol unit 14 concludes (or determines, resolves) an admissibledryness condition, and continues to perform the drying cycle for apreset second additional time D2 (block 230). In other words, ifadmissible dryness condition is detected, the electronic control unit 14continues to perform the drying cycle, after the cycle time TD, for thepreset additional time D2, after which the drying cycle is stopped(block 230).

Preferably the preset additional time D2 depends on the selected dryingcycle.

Preferably, the preset additional time D2 is between 0 and ten seconds;if D2 is 0 seconds, the drying cycle is stopped immediately orsubstantially immediately after the electronic control unit 14 concludes(or determines, resolves) that it has been reached the admissibledryness condition.

According to the preferred embodiment, after stopping of the dryingcycle, electronic control unit 14 may preferably perform a final coolingphase (block 240), wherein drum 3 may be kept turning, and non-heatedair (since the heating device 10 has been permanently switched-off) maybe fed into drum by the fan 11 so as to lower the high temperature to apredetermined low temperature (e.g. 30° C.) at which laundry 5 can behandled by the user.

Regarding what has been described above, it should be pointed out thatthe above-described control method may advantageously be encoded insoftware that can be loaded in the electronic control unit 14 of therotatable-drum laundry drier 1 and designed to ensure that, whenexecuted, the electronic control unit 14 becomes configured forcontrolling the rotatable-drum laundry drier 1 according to theprovisions of the method.

The laundry dryer of the present invention has the following advantages.

The additional detecting phases permit the laundry dryer to improvedetecting the condition of empty-drum or of already-dry laundry loaded,and in this case to immediately stop operating the laundry dryer, so asto decrease wastage of electric energy.

Moreover, increasing of cycle time in case of detection of aninsufficient dryness condition assures uniform laundry dryness, even incase of small load/quantity of laundry, and/or when the latter isarranged inside the rotatable-drum so that number of contacts with theelectrode sensor is very low.

Clearly, changes may be made to the method and the rotatable-drumlaundry dryer as described and illustrated herein without, however,departing from the scope of the present invention.

1. A method of controlling a drying operation of a rotatable-drumlaundry dryer comprising a rotatable drum for loading laundry and atleast one electrode sensor for sensing dryness of the laundry; themethod comprising: detecting the presence/absence of moist laundryinside the rotatable drum by said at least one electrode sensor; upon apresence of moist laundry inside the rotatable drum being detected,starting a drying cycle; sensing dryness of the laundry during saiddrying cycle; measuring a cycle time at which the sensed dryness reachesa preset dryness threshold; upon the measured cycle time being lowerthan a preset dryness threshold time, continuing the drying cycle for afirst additional time, and stopping the drying cycle at the end of saidfirst additional time.
 2. The method according to claim 1, wherein saidfirst additional time is such that the time elapsed from the beginningof said drying cycle to the stopping of the drying cycle is a presetminimum dryness time.
 3. The method according to claim 1, wherein saidfirst additional time is set as the difference between said presetminimum dryness time and said cycle time.
 4. The method according toclaim 1, further comprising: upon said cycle time being not lower thansaid preset dryness threshold time, continuing the drying cycle for apreset second additional time; and stopping the drying cycle at the endof said second additional time.
 5. The method according to claim 4,wherein said second additional time is between zero and ten seconds. 6.The method according to claim 1, wherein determining thepresence/absence of moist laundry inside the rotatable-drum comprises:performing a starting detection phase for a starting detection time;upon no moist laundry being detected during said starting detectiontime, performing one or more additional detection phases, each of whichlasts an additional detection time; and upon no moist laundry beingdetected during said additional detection phase/s, ending operation ofthe rotatable-drum laundry dryer.
 7. The method according to claim 6,wherein said additional detection time is less than said startingdetection time.
 8. A rotatable-drum laundry drier comprising: arotatable drum for loading laundry, at least one electrode sensor forsensing dryness of the laundry; drying air feeding means for feedingdrying air into the drum, and rotation driving means for rotating thedrum about an axis of rotation; and electronic control means configuredto: detect presence/absence of moist laundry inside the rotatable drumby said at least one electrode sensor; if upon a presence of moistlaundry inside rotatable drum being detected, start a drying cycle;sensing dryness of the laundry during said drying cycle; measure a cycletime at which the sensed dryness reaches a preset dryness threshold; andupon the measured cycle time being lower than a preset dryness thresholdtime, continue to perform the drying cycle for a first additional time,and stop the drying cycle at the end of said first additional time. 9.The dryer according to claim 8, wherein said first additional time issuch that the time elapsed from the beginning of said drying cycle tothe stopping of the drying cycle is a preset minimum dryness time. 10.The dryer according to claim 8, wherein said first additional time isset as the difference between said preset minimum dryness time and saidcycle time.
 11. The dryer according to claim 8, wherein said electroniccontrol means are further configured to: continue to perform said dryingcycle for a preset second additional dryness time if upon said cycletime being not lower than said preset dryness threshold time; and stopthe drying cycle at the end of said preset second increased cycle time.12. The dryer according to claim 11, wherein said second additional timeis between zero and ten seconds.
 13. The dryer according to claim 9,wherein said electronic control means are further configured to: performa starting detection phase for a starting detection time; upon no moistlaundry being detected within said starting detection time, perform oneor more additional detection phases; and upon no moist laundry beingdetected during said additional detection phase/s, end operation ofrotatable-drum laundry drier.
 14. The dryer according to claim 13,wherein, each of said one or more additional detection phases lasts anadditional detection time less than said starting detection time. 15.The method according to claim 2, wherein said first additional time isset as the difference between said preset minimum dryness time and saidcycle time.
 16. The method according to claim 2, further comprising:upon said cycle time being not lower than said preset dryness thresholdtime, continuing the drying cycle for a preset second additional time;and stopping the drying cycle at the end of said second additional time.17. The method according to claim 2, wherein determining thepresence/absence of moist laundry inside the rotatable-drum comprises:performing a starting detection phase for a starting detection time;upon no moist laundry being detected during said starting detectiontime, performing one or more additional detection phases, each of whichlasts an additional detection time; and upon no moist laundry beingdetected during said additional detection phase/s, ending operation ofthe rotatable-drum laundry dryer.
 18. The dryer according to claim 9,wherein said first additional time is set as the difference between saidpreset minimum dryness time and said cycle time.
 19. The dryer accordingto claim 9, wherein said electronic control means are further configuredto: continue to perform said drying cycle for a preset second additionaldryness time upon said cycle time being not lower than said presetdryness threshold time; and stop the drying cycle at the end of saidpreset second increased cycle time.
 20. The dryer according to claim 9,wherein said electronic control means are further configured to: performa starting detection phase for a starting detection time; upon no moistlaundry being detected within said starting detection time, perform oneor more additional detection phases; and upon no moist laundry beingdetected during said additional detection phase/s, end operation ofrotatable-drum laundry drier.